You may also want to play "airport" with your kids before you leave.
They will have to put everything they are carrying into the bin to be scanned, including blanket, baby doll, toy, etc. I didn't think of this the time my DD carried her baby doll with her. She was really upset that it was taken away just when she really felt the need for some security.
In addition, you may want to have them practice walking through a doorway in front of you and waiting on the other side in the hall since this is what they will have to do at the airport also. After they walk through, with no "beep", they will then be able to reclaim whatever they put through the "x-ray machine". You might also want to pretend to beep so you could wand them down with a banana or something.
Anything to help aleve their fears ahead of time is helpful.